#include <stdio.h>
int main()
{
    double m = 2.0; //分子
    double n = 1.0; //分母
    double fwd;     //前一项分子
    long i;
    int count;
    scanf("%d", &count);
    double result = 0;
    for (i = 1; i <= count; i++)
    {
        result = m / n + result;
        fwd = m;
        m = m + n;
        n = fwd;
    }
    printf("%.2f", result);
}